PROJECT SUMMARY Candidate: Dr. Toska is steadfast in her commitment to support young women living with HIV in lower- and middle-income countries (LMICs) to survive and thrive, which includes developing interventions that enable them to adhere to ART, engage in healthy sexual relationships, and plan safe pregnancies. Her career development plan focuses on: 1) cultivating scientific expertise to investigate sexual and reproductive health resilience, a concept developed for this award, 2) gaining knowledge on developing socio-behavioral interventions for young women living with HIV, and 3) expanding leadership and mentorship skills. These objectives will be realized through the support of highly-experienced mentors, who are global scientists in research on HIV, adolescents and young people, and sexual and reproductive health in LMICs. Through this award, Dr. Toska will consolidate her career goal of becoming a global leader in socio-behavioral interventions to reduce onward HIV transmission among young people living with HIV in LMICs. Research: Reducing onward HIV transmission among young women living with HIV in LMICs is central to breaking the cycle of transmission, by addressing both vertical (mother-to-child) and horizontal (sexual) transmission to partners. Global HIV prevention efforts to date focus on supporting all people living with HIV to stop onward HIV transmission through viral suppression (Undetectable=Untransmittable). Growing evidence has documented how young women living with HIV experience poorer HIV treatment outcomes, higher rates of unintended pregnancies and greater risk of passing on HIV to their children. No intervention addresses these two aspects of U=U among young women living with HIV. The scientific goal of this K43 is to inform the development of an evidence-based intervention that addresses the complex relationship ?clusters? that young women living with HIV are part of, to reduce onward HIV transmission to their partners and children. The training objective of this K43 is to obtain intensive mentoring and formal training on the foundational skills necessary to develop an evidence-based intervention to stem onward HIV infection among young women living with HIV. The specific research aims of this award are to 1) investigate predictors of onward HIV transmission, 2) develop and validate a quantitative measure for sexual and reproductive health resilience, and 3) map causal pathways between sexual and reproductive health resilience, unintended pregnancies, and viral suppression among young women living with HIV. This award capitalizes on the intellectual and research infrastructure of two existing cohorts, Mzantsi Wakho and HEY BABY, based in the Eastern Cape, South Africa. The study advances NIH priorities by advancing science on HIV transmission in a highly vulnerable population, promoting the development of an evidence-based interventions for HIV prevention for this population, and building capacity for an LMIC emerging researcher and the early career researchers she will collaborate with.